What causes "buffer is empty" in hyperledger/fabric?

Check the caller that builds the block buffer — only invoke verification when at least one block was pulled

buffer is empty

Error message

buffer is empty

What it means

verifyBlockSequence (used by VerifyBlocks / VerifyBlocksBFT) requires a non-empty batch of blocks to verify. An empty slice provides nothing to anchor configuration or signature verification, so it returns this guard error immediately.

Source

Thrown at orderer/common/cluster/util.go:750

		return errors.New("signature invalid")
	}
	return nil
}

func SHA256Digest(data []byte) []byte {
	hash := sha256.Sum256(data)
	return hash[:]
}

// VerifyBlocksBFT verifies the given consecutive sequence of blocks is valid, always verifies signature,
// and returns nil if it's valid, else an error.
func VerifyBlocksBFT(blocks []*common.Block, signatureVerifier protoutil.BlockVerifierFunc, vb protoutil.VerifierBuilder) error {
	return verifyBlockSequence(blocks, signatureVerifier, vb)
}

func verifyBlockSequence(blockBuff []*common.Block, signatureVerifier protoutil.BlockVerifierFunc, vb protoutil.VerifierBuilder) error {
	if len(blockBuff) == 0 {
		return errors.New("buffer is empty")
	}

	// Verify all configuration blocks that are found inside the block batch,
	// with the configuration that was committed (nil) or with one that is picked up
	// during iteration over the block batch.
	for i, block := range blockBuff {
		if err := VerifyBlockHash(i, blockBuff); err != nil {
			return err
		}
		configFromBlock, err := deliverclient.ConfigFromBlock(block)

		if err != nil && err != deliverclient.ErrNotAConfig {
			return err
		}

		if err := VerifyBlockSignature(block, signatureVerifier); err != nil {
			// Genesis blocks are not signed, so silently ignore the error
			if block.Header.Number > 0 {

View on GitHub (pinned to 2736b63f8f)

Solutions

Check the caller that builds the block buffer — only invoke verification when at least one block was pulled
Inspect the slicing/pagination logic that produced blocks[start:end] for an off-by-one empty window
Log len(blocks) at the call site to confirm the batch before verification
In code paths that legitimately receive empty batches, skip verification instead of calling it

Example fix

// before
err := VerifyBlocksBFT(receivedBlocks, verifier, vb) // receivedBlocks may be empty
// after
if len(receivedBlocks) == 0 {
    return nil // nothing to verify
}
err := VerifyBlocksBFT(receivedBlocks, verifier, vb)

Defensive patterns

Strategy: validation

Validate before calling

if len(blocks) == 0 {
    return errors.New("nothing to verify: block batch is empty")
}

Type guard

func hasBlocks(blocks []*common.Block) bool { return len(blocks) > 0 }

Try / catch

err := cluster.VerifyBlocksBFT(blocks, verifier, vb)
if err != nil && strings.Contains(err.Error(), "buffer is empty") {
    logger.Warning("received empty block batch; skipping verification")
    return nil
}

Prevention

Guard call sites with len(blocks) > 0 before verification
Review slicing expressions blocks[i:j] for empty windows
Log batch sizes at pull/filter time
Return early on empty pull results instead of delegating to the verifier

When it happens

Trigger: Calling VerifyBlocks or VerifyBlocksBFT with a zero-length []*common.Block slice — e.g. a Replicator feeding an empty block buffer pulled from an empty filter result, or a caller that already drained the buffer before verification.

Common situations: Custom replication/consenter logic passing filtered block slices that ended up empty; off-by-one slicing (blocks[start:end] with start==end); wiring a nil/empty buffer in tests.

Related errors

AI-assisted analysis of hyperledger/fabric@2736b63f8f (2026-09-04). Data as JSON: /api/errors/534504aa54e94645. Report an issue: GitHub.